To produce oil or gas, a well is drilled into a subterranean formation that is an oil or gas reservoir.
Well Servicing and Well Fluids
Generally, well services include a wide variety of operations that may be performed in oil, gas, geothermal, or water wells, such as drilling, cementing, completion, and intervention. Well services are designed to facilitate or enhance the production of desirable fluids such as oil or gas from or through a subterranean formation. A well service usually involves introducing a well fluid into a well.
Well services can include various types of treatments that are commonly performed in a wellbore or subterranean formation.
For example, a treatment for fluid-loss control can be used during any of drilling, completion, and intervention operations. During completion or intervention, stimulation is a type of treatment performed to enhance or restore the productivity of oil and gas from a well. Stimulation treatments fall into two main groups: hydraulic fracturing and matrix treatments. Fracturing treatments are performed above the fracture pressure of the subterranean formation to create or extend a highly permeable flow path between the formation and the wellbore. Matrix treatments are performed below the fracture pressure of the formation. Other types of completion or intervention treatments can include, for example, gravel packing, consolidation, and controlling excessive water production. Still other types of completion or intervention treatments include, but are not limited to, damage removal, formation isolation, wellbore cleanout, scale removal, and scale control. These and other types of well treatments and treatment fluids are known in the art.
Problems with Using Acids in Well Fluids
Acids are commonly needed in well fluids for various well services.
A problem associated with using acidic well fluids is the corrosion caused by the acidic solution to any metal goods (such as tubular goods) in the well bore and the other equipment used to carry out the treatment. Acidic fluids have a tendency to corrode tubing, casing, and downhole equipment, such as gravel pack screens and downhole pumps, especially at elevated temperatures. The expense of repairing or replacing corrosion-damaged equipment is extremely high. The corrosion problem is exacerbated by the elevated temperatures encountered in deeper formations. The increased corrosion rate of the ferrous and other metals comprising the tubular goods and other equipment results in quantities of the acidic solution being neutralized before it ever enters the subterranean formation, which can compound the deeper penetration problem discussed above. In addition, the partial neutralization of the acid with metal goods can result in the production of quantities of metal ions that are highly undesirable in the subterranean formation.
Another problem associated with acids in well fluid is that the acids or the acidic well fluids can pose handling or safety concerns due to the reactivity of the acid. For instance, during a conventional acidizing operation, corrosive fumes may be released from the acid as it is injected down the well bore. The fumes can cause an irritation hazard to nearby personnel, and a corrosive hazard to surface equipment used to carry out the operation.
Although acidizing a portion of a subterranean formation can be very beneficial in terms of increasing the permeability of the formation to fluid flow, conventional acidizing systems have significant drawbacks. One major problem associated with conventional acidizing treatment systems is that deeper penetration into the formation is not usually achievable because, inter alia, the acid may be spent before it can deeply penetrate into the subterranean formation. The rate at which acidizing fluids react with reactive materials in the subterranean formation is a function of various factors including, but not limited to, acid concentration, temperature, fluid velocity, mass transfer, and the type of reactive material encountered. Whatever the rate of reaction of the acidic solution, the solution can be introduced into the formation only a certain distance before it becomes spent. For instance, conventional acidizing fluids, such as those that contain organic acids, hydrochloric acid or a mixture of hydrofluoric and hydrochloric acids, have high acid strength and quickly react with the formation itself, fines and damage nearest the well bore, and do not penetrate the formation to a desirable degree before becoming spent. To achieve optimal results, it is desirable to maintain the acidic solution in a reactive condition for as long a period as possible to maximize the degree of penetration so that the permeability enhancement produced by the acidic solution may be increased. Alternatively, a delayed release of an acid can be useful.
Therefore, among other needs, there is a need for fluids and methods that reduce the problems of using acids.